Technical cinquecento cooling fan doesn't cut in early enough

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Technical cinquecento cooling fan doesn't cut in early enough

pm215

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My 900cc Cinquecento seems to have developed a tendency to overheat in traffic because the cooling fan doesn't cut in early enough. After coming home from a recent test run I let it sit on the drive for ten minutes or so, and the temperature was heading past 120C (by the internal gauge) with no sign of the fan; so I turned off the engine to stop it overheating and *then* the fan comes on... (Water was coming out past the expansion tank cap, so it's not just that the temp gauge is lying to me; the engine really is too hot.)

It's not the temperature sensor thingy, because I tried changing that with no effect (and testing the old and new ones with the aid of a pan of boiling water and a thermometer showed them both going to zero resistance at the 90-somethingC they're supposed to). And it's not that the fan doesn't work at all, because it does come on eventually. Another thing it definitely isn't is the thermostat, because I've just replaced that for being stuck open (with the old stat the car was running way under temp on motorways and then overheated when you stopped).

So I'm a bit stuck as to what else the problem could be -- can anybody suggest anything else?

Thanks in advance
-- Peter
 
Hi, i bought my Cinq sporting with the headgasket gone (usually a cause of overheating) and it seemed the thermostat played a part in this as it was stuck. I had to replace this on my old Panda 750 fire aswell, they tend to corrode inside with age so its probably a likely cause. They only cost 20 or so pound so its not too expensive to do. As i say it may not fix it, but its probably worth trying it once you have checked all the easy things.
 
fingers99: worth a try, I guess. (Why only the earth cable, by the way?)

rallycinq: The garage tried the new-cap approach last year; didn't help. (Also, wouldn't you need a duff cap *and* a misreading temp gauge to get these symptoms?) I believe it's been bled properly (although since there's no bleed screw on the heater pipe it's a pig to get the air out of the top section with the cabin heater matrix in it). At least, I did what the Haynes manual says you should do, and all the bits seem to be getting hot properly...
 
slosei: water pump: is there an easy test for that?

Dead pump would mean no or very little coolant flow, right? It definitely wasn't overheating during motorway driving, which suggests that the rad can cool the engine if there's air flow through it -- I'd have thought that if the pump had gone air flow through the rad wouldn't make much difference.
 
I dont really know how the check the water pump tbh but on my cinque i had a similar problem on local runs but fine on motorways and it vanished after i changed the water pump i also flushed the coolant system
 
I have the same problem with my 1.1 Sporting. The temperature guage gets to 110 and the fan sometimes doesn't come on even though it is set to switch on at 70 (as I live in Spain and at the moment its 30ish degrees). Then when I stop the water is gushing out of the cap. I took it to the mechanic who said the cap needs replacing but when it was screwed on really tight the water did not escape but STILL the temperature was way too high. I am constantly watching the gauge to see if it gets to 120 (which it did last week). The thermostat has been changed and the water pump was replaced last year. The fan switch was also changed last year. I never had a problem with the temperature for 7 years before a mechanic in Spain worked on it. I am not very practical with cars but with the right guidance I'll have a go. Alas my Haynes manual is in the UK so I am a bit lost. I can't really "use" the car, only on short trips in case the worse happens. The coil packs have been replaced because of the overheating.
 
I had an idea for narrowing down the problem -- disconnect the cable to the temperature switch and attach a multimeter instead. Then you can see whether or not the resistance drops as the car heats up, which ought to indicate whether the problem is on the fluid or the electrical side. Then as a followup you can short the cable with a suitable bit of wire to confirm that when the fan runs it does keep the engine cool enough (or not). I'll try to get round to trying this in the next few days.
 
Change the cap, and make sure its properly bled.

And enough coolant in the first place.

slosei: water pump: is there an easy test for that?

Dead pump would mean no or very little coolant flow, right? It definitely wasn't overheating during motorway driving, which suggests that the rad can cool the engine if there's air flow through it -- I'd have thought that if the pump had gone air flow through the rad wouldn't make much difference.

What about the thermostat? Would that sticking shut cause the lack of coolant circulation, and the overheating?

Jon.
 
Had a similar prob a few weeks ago...
I gave the rad a really good flush with a hose in both inlet and exit points and the prob has gone...also it used to run at 70deg and now runs at 85deg most of the time.
I think Cinqs are close to the edge cooling wise and any small prob makes them do all sorts of weird things
 
Thanks to those suggesting the water pump. I noticed today that when the engine is idling the air from the cabin heater gets noticably cooler (that is, when you're running at above idle there's lots of warm-to-hot air, sit at idle for ten seconds and it's barely warm). That seems to me to suggest that water isn't really circulating at idle and does rather point the finger at the pump.
 
Right, I just did a test -- on the driveway, and with the temp sensor disconnected and the cable set up so I could turn the fan on manually (good old bent paperclip). I let it get up to an indicated 110C or so, top tube hot so thermostat definitely open, and turned on the fan with the paperclip. Result: no obvious effect on temp gauge. Rev the engine a bit, and gauge rapidly drops to 90C or thereabouts. I'm now fairly certain it is indeed the water pump.

Thanks to all for the advice.
 
i perfectly know what you talking about. my mechanic suggested to clean the rad with water and air pressure. rads get dirty after a long period of its use and their could be blockages from the coolant itself. i just hope that this works out for me as i live in malta and the temperature is quite high.
 
Having spent this morning replacing what turned out to be a perfectly good water pump a radiator blockage is next on my list of suspects, yes...
 
i have recently had problems with my cinq overheating in traffic and have eliminated everything apart from the cooling fan switch. can any1 tell me how to test is as i tried putting it in boiling water and testing the resistance on the pins with a multimeter with no effect to the switch activating. however i then replaced the switch with no effect and wondered if there was a more effective way to test the switches????
 
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